DCD: In the double chromodomain (DCD), both chromodomains share their general secondary structure elements with those previously seen in HP1 and Polycomb chromodomains. The linker segment forms a novel helix–turn–helix structure that juxtaposes the two chromodomains to form a continuous surface. A total of 350 Å is buried at the interface of these tandem chromodomains. (1)